Question: Simplify the following expression: $9\sqrt{8}$.
Explanation: First, try to factor a perfect square out of the radical. $= 9\sqrt{8}$ $= 9\sqrt{4 \cdot 2}$ Separate the radical and simplify. $= 9\sqrt{4} \cdot \sqrt{2}$ $= 9 \cdot 2 \cdot \sqrt{2}$ $= 18\sqrt{2}$